A number of systems for converting sunlight to electricity are known. One such system that has proven useful in efficiently producing electricity from the sun's radiation is described in U.S. Pat. No. 4,691,076. In that system, an array is formed of semi-conductor spheres. Each sphere has a P-type interior and an N-type skin. A plurality of the spheres are housed in a pair of aluminum foil members which form the contacts to the P-type and N-type regions. The foils are electrically insulated from one another and are flexible. Multiple arrays can be interconnected to form a module of solar cell elements for converting sunlight into electricity.
In order to produce sufficient quantities of the arrays, it is necessary to have a process for their manufacture that is uncomplicated, low cost and efficient. An uncomplicated system would be one using currently available technology constructed in such a way that the applicable process steps can be conducted in a highly repeatable manner. Moreover, the less complicated the process steps, generally the more cost effective will the entire process be carried out. Finally, the more repeatable the process, the more efficiently the operation and the higher production of solar arrays.
A key process step in the making of silicon solar cells is affixing the silicon spheres to a foil matrix. A known technique for bonding silicon spheres to a aluminum foil is to heat the foil to a temperature slightly below the eutectic point (approximately 570.degree. C.) and then compress the spheres into the foil by using a free falling weight. The free falling weight generates sufficient shear forces at the silicon and aluminum foil interface to form good adhering bonds.
Drop weight bonding has numerous problems and disadvantages. First, the technique is inherently slow. Second, the drop weight approach does not lend itself to scaling up for larger production volumes. Another problem with drop weight bonding is that distortions in the impact surface of the weight result in undesirable center pressures. Finally, the technique results in too many damaged spheres and shorted cells.